The interaction of antigen-specific T cells from a highly enriched population with antigen-pulsed macrophages will be studied. Both the guinea pig and mouse will be used to supply cells. We will continue to attempt isolation and characterization of the antigen-specific receptor from the T lymphocyte and to ascertain the molecular mechanisms and organelle requirements responsible for the observed binding of the 2 cell types. Immuno-electron microscopy will be used to map the antigen on the macrophage surface. The structural differences between secreted and cell surface mu chain will be pursued. An attempt will be made to determine if there is a peptide difference between the two forms of the molecule that could account for the capacity of surface IgM to bind to the plasma membrane. The nature of antigenic recognition by killer T cells will be further studied by a combination of genetic and structural techniques. For example, using the TNP system, the derivatized H-2 molecule will be cleaved by proteolytic enzymes to determine which portion of the molecule contains antigenic determinants recognized by T cells. The structural relationships among products of chromosome 17 in the mouse will be analyzed at the level of primary structure and antigenicity.